White Paper
Quality and an attractive price
– The right way to buy valves/valve terminals –
The global market for valves and valve terminals today is so large that it is almost
impossible to maintain an overview. Often, price seems the only buying criterion. But it
pays to look more closely, particularly with regard to higher productivity and process
reliability. Users of Festo's attractively priced and long-lasting high-quality valves
benefit in tough everyday practical applications from the meticulous development
processes, including numerous simulation tests and the correct choice of technologies
and materials.
This white paper provides information on:
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Care pays for itself: the development process of valves and valve terminals
Caution: not all manufacturer data is comparable 1 to 1!
Small differences with a great impact: how to choose the right valves/valve terminals
An overview of good practice: the
development process of valves and valve
terminals
Once these tests have been concluded successfully, a
quality release is issued for the product concept.
Work also starts on complete technical product
documentation. This is followed by -testing of the
assembly system and production process (phase 3).
This phase includes the verification of suppliers and
ordering processes, updating of master data and
transferring this into the production system and
preparations for the market launch. The final
milestone in this phase, "Pilot series release", marks
the start of phase 4, pre-production.
The development of a valve by Festo or other
comparable companies takes on average three years.
Good results and high quality depend on all kinds of
processes carried out in various different
departments.
Phase 1 of development is concerned with preprocess strategy. In this phase, market requirements
are evaluated on the basis of future scenarios. Ideas
and suggestions are generated by Festo Product
Management, customers as well as networks of jointventure partners such as universities. The project
team uses this input to produce the performance
specifications. After the clarification, planning and
approval stages, the product specifications can be
put together, including a project plan, a solution, a
budget, a test schedule, a general timeline, etc. In
addition to covering functionality and product
dimensions, the solution must also consider
ergonomics, ease of operation and a uniform product
design.
This phase covers another review of service-life tests,
building up product stocks and initial marketing
activities. It also covers training for sales staff. The
start-up of series production is followed by a product
audit. This comprises quality, internal and external
complaints, ability to deliver, on-time delivery and
customer feedback. The results are summarised in a
final project report.
Questions which customers should ask themselves
If you are planning to buy valves and have two or
more quotations with comparable prices, your choice
should be guided not only by component price but
also the total cost of ownership and the competence
of the suppliers. A careful development process is
particularly important when large quantities of
products are to be installed in harsh environments. In
those cases, you should ask yourself the following
questions:
During the subsequent product realisation process
(phase 2), a CAD model is produced on the basis of
the product specifications and the flow and material
optimisation processes. This model can then be used
to create detailed and individual component
drawings. These are used for a first FMEA analysis 1.
After an initial evaluation of the manufacturing and
assembly process, advance quality planning can
begin. As soon as the first close-to-series test
samples are produced, a number of tests and
inspections are carried out, such as:
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Vibration and shock tests to assess the
behaviour of the valves during transport or
when installed on a dynamic robot arm.
Examination of valve behaviour to identify
possible reciprocal effects within temperature,
voltage or pressure ranges.
IP inspections, preceded by alternate hot/cold
exposure tests, to ensure that everything
works correctly even at extreme temperatures.
Tests of valve terminals fitted with all the
equipment in order to test flow rates or backpressure surges when several valves are
actuated simultaneously.
Scans using computer tomography to detect
problems such as cavities in valve housings at
an early stage
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In the following section you will find a description of
a small selection of the engineering tools used by
Festo during development. In order to obtain the best
possible results when developing valves/valve
terminals, Festo also uses a wealth of other specially
developed software tools, together with an excellent
collection of test and inspection equipment, such as
an EMC laboratory, computer tomography and a well
equipped materials test laboratory.
FMEA, Failure Mode and Effects Analysis
© Copyright 2013, Festo AG & Co. KG
What tools have been used in the
development process in order to achieve
optimum product design?
What tests and inspections have been
carried out?
Do the results of these tests and inspections,
when used as the basis for data sheets,
allow an equal comparison with other
manufacturers' data?
Have test series been carried out only to
verify the values required by the relevant
standard? Or have further tests and
inspections also been carried out, for
example to assess reciprocal effects?
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From standard programs to in-house developments: not every manufacturer uses
sophisticated software tools to ensure the highest quality of the end product!
Tools
Area of application and customer questions
Simulation of
structural
mechanics
Structural mechanics is used for the computation of deformations, forces and internal
stresses in components to prevent damage and leakage problems. The program
provides answers to questions such as:
• Has allowance been made for housing deformations occurring during the assembly
process? Have safety factors been included?
• What happens with highly dynamic working pressures? Can these result in cracking or
settling, in turn leading to leakages?
Simulation of
thermal influences
Thermal simulation helps to design valves/valve terminals that can withstand extreme
situations and prevent failure through overheating. The program provides answers to
questions such as:
• 100% duty cycle, fast switching position changes, welding environments, cleaning
cycles or warm air can lead to temperature rises on printed circuit boards and/or on
valve terminals. Can the valves withstand these effects?
• Has the circuit been selected correctly and have the components been placed correctly
on the printed circuit board?
• Have the correct materials been selected with regard to the temperatures involved?
Simulation of air
flow
Flow simulation is essential in order to obtain maximum flow rate performance and the
most efficient valves possible. The program provides answers to questions such as:
• Can droplet formation occur in the valve due to its geometrical shape?
• It is crucial for high energy efficiency that flow rates are as high as possible and
pressure drops are as low as possible. Has this been taken into account?
• Have the flow-related loads that affect components (e.g. pistons) and that may lead to
increased valve wear been determined?
Simulation of seal
behaviour
Freedom from leaks is crucial for reliable valve operation. The Shore hardnesses of the
seals affect this. The program provides answers to questions such as:
• Thermal expansion of the housing and inadequate seal tolerances with high Shore
hardness can cause micro leaks. Has allowance been made for this?
• What happens to sealing rings at high operating pressures (e.g. 10 bar) or with dualpressure operation (vacuum/compressed air)? Can deformations occur, leading to
leaks?
Simulation of
injection moulding
or die casting
A simulation of the casting process helps to assess quality and ensure a reliable
production process. The program provides answers to questions such as:
• Do cavities develop in the housing during the cooling process? In the course
of subsequent spot tests, for example using computer tomography, the points
with an especially high number of cavities are closely investigated.
• Component twisting resulting in deformation tolerances can cause leaks. Have
simulations been carried out to determine optimum tolerances?
• How were the moulding point, degree of distortion, joins, glass fibre
orientation and degree of shrinkage determined in order to ensure a stable
manufacture process in subsequent series production?
Table 1: Development tools and data gathering
© Copyright 2013, Festo AG & Co. KG
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Not all manufacturer data is comparable 1 to 1! – The important points to bear in mind –
If you need a heavy-duty valve terminal for use in a welding environment, metal will be the preferred material. If, on
the other hand, a valve needs to be lightweight or corrosion resistant or is intended for an application where low
electrical conductivity is necessary, the recommendation will usually be for a plastic valve. When you compare
quotations, you should not look only at the price as the various types of plastic are not all the same. In many cases,
too, data-sheet values will not be comparable 1 to 1. Here is a short list of points to bear in mind.
Plastics
Plastics are today's promising materials for the
future. And while alloys are standardised with regard
to their composition and technical characteristics,
there is no such standardisation for plastics. There
may therefore be significant differences between
different media with regard, for example, to stress
crack formation or creep behaviour at higher
temperatures. Any price difference between
comparable products may be due to the fact that a
high-tech polymer has been used for one of the
products, which may be useful under specific
climatic conditions or when the product needs to be
resistant to cleaning agents used in the food
industry.
switching travel. You should therefore ask the
manufacturer whether response times have been
determined in accordance with the specifications of
ISO 12238 or whether another standard such as JIS B
8375-1981 has been used.
European manufacturers usually measure in
accordance with ISO 12238. This measures the
switching time as the time taken from the moment a
switching pulse has been triggered until 10% of the
defined measuring pressure has been reached.
Minimising risk through further tests
Today, high quality is a must for every valve
manufacturer. What varies greatly between
manufacturers is the number and variety of tests and
the equipment available. Not every supplier has its
own EMC laboratory, scanning electron microscopes,
computer tomographs etc.
Leak testing and IP classification
Leak testing and IP classification are carried out
under standardised conditions. You should ask the
manufacturer whether he can demonstrate that tests
beyond the requirements of the relevant standard
are carried out. For example, Festo conducts
exposure tests before leak testing and IP
classification. During these tests, components are
exposed to changing temperatures in order to
investigate factors such as creepage with plastics.
This is the only way to guarantee that a boltedtogether plastic valve will remain leakproof when
subjected to varying temperatures and the
associated and setting processes.
Fig. 1: Testing the electromagnetic compatibility of valves in
Festo's EMC laboratory
Flow data
Always check when comparing flow rate data that
this is based on the same standard, such as ISO
6358, and that data has been measured or
converted in accordance with this standard.
Festo, for example, carries out flow tests with valve
terminals fitted with their maximum equipment level,
not just with single valves. This allows precise
measurement of back pressures or pressure drops
when several valves are actuated simultaneously.
Tests in areas such as extreme temperature, control
voltage or maximum pressure are also carried out as
standard. You should also consider whether or not
additional quality tests of this kind have been
carried out choosing valves/valve terminals. This is
particularly important in industries such as the
automotive industry where every hour of downtime
costs several thousand euros.
Switching times
Not all manufacturers have the same views when it
comes to ways of defining switching times. Switching
times always start with the triggering of a switching
pulse, but the definition of the end of the switching
time varies. Some manufacturers quote the time until
the standard nominal flow rate is reached, or at least
a certain percentage of this, while others take the
time until the control slide has completed its full
© Copyright 2013, Festo AG & Co. KG
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Small differences in your choice of valves/valve terminals - with a great impact!
As a decision-maker, you know your interests. At the same time, you should not forget the needs of your end
customers or equipment suppliers. As a basic principle, valves or valve terminals must meet the necessary
technical requirements such as flow rate, function, available installation space, IP class etc. The section below
advises you on what other factors you should bear in mind.
Exploiting modularity to implement optimizations
Different customer applications or requirements
often use different electrical interfaces. For
example, there may be a bus system in one
installation and the common low-cost multi-pin
connector solution in another. Would you like to
avoid any possible space problems in your control
cabinet or in your installation and be able to use the
same mounting holes every time? Then you should
ensure that, even with changing electrical
interfaces, the footprint of your valve terminal
remains constant.
l/min. (for approx. 13 valves each consuming 300
l/min.), the resulting pressure loss Δp will be 1.25
bar. With a 40 µm filter, this pressure loss Δp will be
considerably smaller. In order to achieve a
secondary pressure of 6 bar, the primary pressure
only needs to be increased by 0.85 bar. This
difference of nearly 50% will be reflected in a saving
of air consumption. The costs savings possible with
a pressure loss of 1 bar and a holding current
reduction circuit can be seen in the column
"Reducing pressure losses and electricity
consumption" by clicking on the brochure:
Does a customer wish to expand the installation
and does the valve terminal need to vacuum
compatible? Or do you simply need an additional
pressure zone with low pressure? In this case, it can
be helpful to have a simple and fast means of
changing between external and internal pilot air.
This is the only way of avoiding the potential
problem of not having sufficient pilot pressure for
the valve.
>> Energy efficiency@Festo – Solutions for a
profitable and sustainable future <<
In those cases where valves are triggered via a bus
system, it can be interesting to have expansion
options which can turn a central installation
concept into a decentralised concept. This can
provide a solution if you have problems with cycle
times – and this changeover can be made even after
the system has been installed.
Fig. 2: Table on page 12 with energy efficiency calculation
Pressure zones are another way of optimising air
consumption. Low-cost seals allow you to match
the air flow precisely to varying requirements.
Check the maximum possible number of pressure
zones.
To sum up: check that the valve terminal you
choose has options for expansion. This can save
you having to buy a new valve terminal.
Manufacturers such as Festo also offer reverse
valve operation. By using two different pressures
for advance and return strokes, you can achieve a
further energy saving (of up to 50% compared with
standard operation). At the same time, exhaust
capacity and speed are also increased.
Cutting energy costs
Energy costs are an ever more important factor in
production operations. With valve terminals, the
crucial factor is the cost of compressed air. Powersaving functions for valve actuators are a good idea
and important for thermal reasons, but the
potential for cutting energy costs is much less than
with compressed air. With regard to pneumatic
components, you should consider what air quality is
specified for your valves/valve terminals. If, for
example, the air quality specification calls for a
maximum particle size of 5 µm, the necessary finemesh filters will cause considerably higher pressure
losses. The graph on page 6 shows that with a
primary pressure of 6 bar and a flow rate of 4000
© Copyright 2013, Festo AG & Co. KG
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If you need manual overrides on valves for
adjusting cylinder sensors or other operations, the
detenting type is very helpful. However, these can
also represent a risk for service technicians and
general safety. A valve whose manual override has
been left detented by a technician during
commissioning can lead to a lengthy search for
software or electrical problems, while careless
pressing the wrong manual override can result in a
safety risk for people and machines. If you wish to
avoid these situations, make sure the solutions you
choose allow changes to be made simply and
conveniently even after installation, for example by
making it possible to turn a detenting manual
override into a non-detenting one or disabling
manual overrides completely.
Air
Air quality/degree
quality/degree of
of filtration
filtration 5μm
5μm
Air
40μm
Air quality/degree
quality/degree of
of filtration
filtration 40μm
Backup: a reserve to deal with surprises
If you are building an installation or machine for the
first time or if you often need to provide for
individual customer wishes on a series-produced
machine, it is advisable to have one or two reserve
valve positions and options on a valve terminal.
Note how many valve positions are available with a
fixed-grid or modular valve terminal and whether a
size mix of valves or vacuum operation is possible.
That will enable you to react quickly if you need an
additional valve or the flow rate of the current valve
provides to be too small, and the cylinder therefore
advances too slowly or if, unexpectedly, vacuum is
required. Make sure you compare the performance
of the valves of different manufacturers and their
suitability for vacuum.
Graphs 1: pressure losses with 5 µm and 40 µm filters
Servicing for an easier life
Would you like to minimise servicing times and
costs as well as installation times? Then good, clear
labelling of pneumatic and electrical connections is
a must. Check whether you can fit label holders.
This reduces the time spent searching for
connections. And there is no need to drill additional
holes for label holder attachments.
You should also check the maximum permissible air
pressure on a valve terminal. Otherwise, if you
suddenly need an operating pressure higher than
the usual 6 bar, this may be a problem. You should
therefore choose standard solutions which go up to
10 bar. This provides you with a safety margin
which offers options for higher performance. A
pressure which has inadvertently been set too high
can also cause leaks at valves, thus shortening their
service life. With a standard 10 bar pressure, you
may in certain cases even be able to use a smaller
valve, which saves space and money. A 10-bar
standard will significantly reduce the number of
complaints received because of valve problems.
Visual aids such as LEDs or QR codes provide
additional help in identifying and correcting a
problem faster. Products can now be identified
quickly, easily and reliably with a barcode/QR code
reader on a mobile phone. This virtually eliminates
mistakes when buying spare parts. What is more,
features such as captive screws and seals, larger
bolt heads etc. make the work of service technicians
easier. These features should be available not only
in special configurations but as standard – after all,
looking for a lost securing bolt in or under a large
machine frame when changing a valve costs
unnecessary time and energy.
Fig. 3: Try out this sample QR code out by simply scanning it with
your smartphone
© Copyright 2013, Festo AG & Co. KG
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Be on the safe side with quality – taking a close look is well worthwhile!
Even very low-cost valves and valve terminals vary greatly in quality. A decision in favour of high-quality
valves and valve terminals in this price bracket does not have to mean substantially higher cost – it may even
be less expensive. By choosing extremely well-tested material properties, a high degree of modularity and a
wealth of standard features such as 10-bar operation, it is possible to prevent many problems. For example,
where an actuator actually needs a pressure of more than 7 bar, or if there is a need to switch vacuum or
speed up a process by reversing operation in order to exhaust a cylinder faster.
Criteria for installation operators
The main criteria affecting the decisions of end
customers are usually factors such as energy
efficiency, services, fast product documentation
using QR codes, process reliability and long service
life backed up by manufacturers' R&D tests, and fast
availability.
There are therefore a number of questions that you
should put to component suppliers to make sure that
you feel you have made the right choice of valve or
valve terminal. These questions relate both to the
development process and the choice of materials,
and also to detailed and comparable manufacturer
data, the selection of the best valve design for a
given application and other characteristics. The range
of services which a manufacturer can offer and the
available safety margins may also be used as criteria
in choosing better products.
Criteria for OEMs
Of course OEMs want to meet the requirements of
system operators. Above and beyond this, they
generally attach great importance to a high degree of
modularity, which reduces the need to keep supplies
of spare parts while it also enables them to react
quickly to requests for expansion options and
additional functions.
These factors very quickly generate a savings effect,
particularly for users who install large quantities of
valves or valve terminals. For OEMs, this fact is a
good argument to use with customers – and gives the
security of knowing that high-quality products mean
a significant reduction in the numbers of complaints.
Good advice which helps users to choose optimum
solutions with an excellent price/performance ratio
always pays for itself.
Fig. 4: Valve terminal VTUG for pressures up to 10 bar, with manual
override capable of subsequent modification, a CTEU fieldbus node
and a label holder
Publisher/author:
Festo AG & Co. KG
Philipp Wahl
Marketing Concepts
Email: pwhl@de.festo.com
Your local contact:
Details can be found
on the website of
your national Festo company.
© Copyright 2013, Festo AG & Co. KG
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